BESS Working Group R. Sharma, Ed.
Internet-Draft A. Banerjee, Ed.
Intended status: Standards Track A. Sajassi
Expires: December 27, 2018 L. Krattiger
R. Sivaramu
Cisco Systems
June 25, 2018
Multi-site EVPN based VXLAN using Border Gateways
draft-sharma-bess-multi-site-evpn-00
Abstract
This document describes the procedures for interconnecting two or
more BGP based Ethernet VPN (EVPN) sites in a scalable fashion over
an IP-only network. The motivation is to support extension of EVPN
sites without having to rely on typical Data Center Interconnect
(DCI) technologies like MPLS/VPLS. The requirements for such a
deployment are very similar to the ones specified in RFC 7209 --
"Requirements for Ethernet VPN (EVPN)".
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 27, 2018.
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Multi-Site EVPN Overview . . . . . . . . . . . . . . . . . . 4
3.1. MS-EVPN Interconnect Requirements . . . . . . . . . . . . 4
3.2. MS-EVPN Interconnect concept and framework . . . . . . . 5
4. Multi-site EVPN Interconnect Procedures . . . . . . . . . . . 7
4.1. Border Gateway Discovery . . . . . . . . . . . . . . . . 7
4.2. Border Gateway Provisioning . . . . . . . . . . . . . . . 8
4.2.1. Border Gateway Designated Forwarder Election . . . . 9
4.2.2. Anycast Border Gateway . . . . . . . . . . . . . . . 9
4.2.3. Multi-path Border Gateway . . . . . . . . . . . . . . 10
4.3. EVPN route processing at Border Gateway . . . . . . . . . 10
4.4. Multi-Destination tree between Border Gateways . . . . . 12
4.5. Inter-site Unicast traffic . . . . . . . . . . . . . . . 12
4.6. Inter-site Multi-destination traffic . . . . . . . . . . 13
4.7. Host Mobility . . . . . . . . . . . . . . . . . . . . . . 13
5. Convergence . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. Fabric to Border Gateway Failure . . . . . . . . . . . . 13
5.2. Border Gateway to Border Gateway Failures . . . . . . . . 13
6. Interoperability . . . . . . . . . . . . . . . . . . . . . . 13
7. Isolation of Fault Domains . . . . . . . . . . . . . . . . . 14
8. MVPN with Multi-site EVPN . . . . . . . . . . . . . . . . . . 14
8.1. Inter-Site MI-PMSI . . . . . . . . . . . . . . . . . . . 14
8.2. Stitching of customer multicast trees across sites . . . 15
8.3. RP placement across sites . . . . . . . . . . . . . . . . 15
8.4. Inter-Site S-PMSI . . . . . . . . . . . . . . . . . . . . 15
9. Observations with Multi-site EVPN . . . . . . . . . . . . . . 15
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
12. Security Considerations . . . . . . . . . . . . . . . . . . . 16
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
13.1. Normative References . . . . . . . . . . . . . . . . . . 16
13.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Additional Stuff . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
BGP based Ethernet VPNs (EVPNs) are being used to support various VPN
topologies with the motivation and requirements being discussed in
RFC7209 [RFC7209]. EVPN has been used to provide a Network
Virtualization Overly (NVO) solution with a variety of tunnel
encapsulation options in RFC8365 [RFC8365] for the Data center
interconnect (DCI) at the WAN Edge. Procedures for IP and MPLS hand-
off at site boundaries are additionally discussed in [DCI-OVERLAY].
In current EVPN deployments, there is a need to segment the EVPN
domains within a Data Center (DC) primarily due to the service
architecture and the scaling requirements around it. The number of
routes, tunnel end-points, and next-hops needed in the DC are
sometimes larger than the capability of the hardware elements that
are being deployed. Network operators would like to inter-connect
these domains without using traditional DCI technologies. In
essence, they want smaller multi-site EVPN domains with an IP
backbone. Additionally, they would like to have an Anycast model for
the nodes at the gateways. This alleviates the hardware of having to
support multi-path on overlay reachability.
Network operators today are using the Virtual Network Identifier
(VNI) to designate a service. They would like to have this service
available to a smaller set of nodes within the DC for administrative
reasons; in essence they want to break up the EVPN domain to multiple
smaller sites. An advantage of having a smaller footprint for these
EVPN sites results in fault isolation domains being constrained. It
also allows for re-use of VNI space across sites.
In a traditional leaf-spine architecture, it is conceivable, that the
network operator may decide to support both the Route-Reflector and
Gateway functionality on the spine nodes. In such a deployment
model, it is necessary to have a site identifier marked with each
domain, such that route import and export rules can work effectively.
In this document we focus primarily on the VXLAN encapsulation for
EVPN deployments, with the underlay providing only IP connectivity.
We describe in detail the IP/VXLAN hand-off mechanisms to
interconnect these smaller sites within the data center itself, and
refer to this deployment model as multi-site EVPN (MS-EVPN). The
procedures described here go into substantial detail regarding
interconnecting Layer-2 (L2) and Layer-3 (L3) networks, for unicast
and multicast domains across MS-EVPNs. In this specification, we
also define the use of the Type 5 Ethernet Segment Identifier (ESI)
(Section 5 of RFC7432 [RFC7432]) between multiple sites using the
Anycast routing model.
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1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology
o Border Gateway (BG): This is the node that interacts with nodes
that are internal to a site and external to it. It is responsible
for functionality related to traffic entering and exiting a site.
o Anycast Border Gateway: A virtual set of shared BGs acting as
multiple entry-exit points for a single site.
o Multipath Border Gateway: A virtual set of unique BGs acting as a
multiple entry-exit points for a single site.
o RT-X: Route Type X as defined for various EVPN route types.
3. Multi-Site EVPN Overview
In this section we describe the motivation, requirements, and
framework for the Multi-Site EVPN (MS-EVPN) functionality.
3.1. MS-EVPN Interconnect Requirements
a. Scalability: Multi-Site EVPN (MS-EVPN) should be able to
interconnect multiple sites, allowing for addition/deletion of
new sites or modifying capacity of existing ones seamlessly.
b. Multi-Destination traffic over unicast-only cloud: MS-EVPN
mechanisms should provide an efficient forwarding mechanism for
multi-destination frames by using existing network elements as-
is. A large flat fabric rules out the option of ingress
replication, as the number of replications becomes practically
unachievable due to the internal hardware bandwidth needed.
c. Maintain Site-specific Administrative control: MS-EVPN should be
able to interconnect fabrics from different Administrative
domains. The solution should allow for different sites to have
different VLAN-VNI mappings, use different underlay routing
protocols, and/or have different PIM-SM group ranges.
d. Isolate fault domains: MS-EVPN technology hand-off should have
capability to isolate traffic across site boundaries and prevent
defects to percolate from one site to another. As an example, a
broadcast storm in a site should not propagate to other sites.
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3.2. MS-EVPN Interconnect concept and framework
EVPN with IP-only interconnect is conceptualized as multiple site-
local EVPN control planes and IP forwarding domains interconnected
via a single common EVPN control and IP forwarding domain. Every
node is identified with a unique site-scope identifier. A site-local
EVPN domain consists of EVPN nodes with the same site identifier.
Border Gateways (BGs) are explicitly part of a site-specific EVPN
domain, and implicitly part of a common interconnect EVPN domain with
BGs from other sites. Although a BG has only a single explicit site-
id (that of the site it is a member of, see Section 4.1), it can be
considered to also have a second implicit site-id, that of the
interconnect-domain which has membership of all the BGs from all
sites that are being interconnected. BGs discover each other through
EVPN RT-1 A-D routes and act as both control and forwarding plane
gateway across sites. This facilitates site-local nodes to visualize
all other sites to be reachable only via its BGs.
We describe the MS-EVPN deployment model using the topology as shown
in Figure 1. In the topology there are 3 sites, Site A, Site B, and
Site C that are inter-connected using IP. This entire topology is
deemed to be part of the same Data Center. In most deployments these
sites can be thought of as pods, which may span a rack, a row, or
multiple rows in the data center, depending on the size of domain
desired for scale and fault and/or administrative isolation.
In this topology, site-local nodes are connected to each other by
iBGP EVPN peering and BGs are connected by eBGP Muti-hop EVPN peering
via inter-site cloud. We explicitly spell this out to ensure that we
can re-use BGP semantics of route announcement between and across the
sites. Other BGP mechanisms to instantiate this will be discussed in
a separate document. This implies that each domain/site has its own
AS number. In the topology, only 2 border gateway per site are
shown; this is more for ease of illustration and explanation. The
technology poses no such limitation. As mentioned earlier, site-
specific EVPN domain consists of only site-local nodes in the sites.
A BG is logically partitioned into site specific EVPN domain towards
the site and into common EVPN domain towards other sites. This
facilitates them to act as control and forwarding plane gateway for
forwarding traffic across sites.
EVPN nodes with in a site will discover each other via regular EVPN
procedures and build site-local bidirectional VXLAN tunnels and
multi-destination trees from leaves to BGs. BGs will discover each
other by RT-1 routes with unique site-identifiers and build inter-
site bi-directional VXLAN tunnels and multi-destination trees between
them. We thus build an end-to-end bidirectional forwarding path
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across all sites by stitching (and not by stretching end-to-end)
site-local VXLAN tunnels with inter-site VXLAN tunnels. In essence,
a MS-EVPN fabric is built in complete downstream and modular fashion.
____________________________
| ooo Encapsulation tunnel |
| X X X Leaf-spine fabric |
|__________________________|
Site A (EVPN site A) Site B (EVPN site B)
___________________________ ____________________________
| X X X X X X X X | | X X X X X X X X |
| X X X X | | X X X X |
| o o | | o o |
|BG-1 Site A BG-2 Site A| |BG-1 Site B BG-2 Site B|
___________________________ ____________________________
o o o o
o o o o
o o o o
o o o o
_______________________________________________
| |
| |
| Inter-site common EVPN site |
| |
| |
_______________________________________________
o o
o o
o o
o o
___________________________
| BG-1 Site C BG-2 Site C|
| X X X X |
| X X X X X X X X |
_____________________________
Site C (EVPN site C)
Figure 1
Site-local tenant domains (for example, bridging, flood, routing, and
multicast) are interconnected only via BGs with site-remote tenant
domains (bridging, flood, routing, and multicast respectively) from
other sites. It stitches such tenant domains (bridging, flood,
routing, and multicast) in complete downstream fashion using EVPN
route advertisements. Such interconnects do not assume uniform
mappings of mac-vrf (or IP-VRF) to VNI across sites.
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4. Multi-site EVPN Interconnect Procedures
In this section we describe the new functionalities in the Border
Gateway (BG) nodes for interconnecting EVPN sites within the DC.
In a nutshell, BG discovery will facilitate termination and re-
origination of inter-site VXLAN tunnels. Such discovery provides
flexibility for intra-site leaf-to-leaf VXLAN tunnels to co-exist
with inter-site tunnels terminating on BGs. Additionally, BGs need
to discover each other such that it is possible to run the Designated
Forwarder (DF) election between the border nodes of a site. It also
needs to be aware of other remote BGs such that it can allow for
appropriate import/export of routes from other sites.
4.1. Border Gateway Discovery
BGs leverage the RT-1 A-D route type defined in RFC7432 [RFC7432].
BGs in different sites will use RT-1 A-D routes with unique site-
identifiers to announce themselves as "Borders" to other BGs. Nodes
within the same site MUST be configured or auto-generate the same
site-identifier. Nodes that are not configured to be a border node
will build VXLAN tunnels only between each member of the site (which
it is aware due to the site-identifier that is additionally announced
by them). Border nodes will additionally build VXLAN tunnels between
itself and other border nodes that are announced with a different
site identifier. The site-identifier is encoded within the ESI label
itself as described below.
In this specification, we reuse the AS-based Ethernet Segment
Identifier (ESI) Type 5 (see Section 5 of RFC7432 [RFC7432]) that can
be auto-generated or configured by the operator. It is repeated here
to illustrate the encoding of the site-identifier.
o Type 5 (T=0x05): The ESI value is constructed with the site-id
parameter being embedded as follows.
* AS number (4 octets). This is an AS number owned by the system
and MUST be encoded in the high-order 4 octets of the ESI Value
field. If a 2-octet AS number is used, the high-order extra 2
octets will be 0x0000.
* Local Discriminator/Site Identifier (4 octets): The Local
Discriminator is also referred to as the Site Identifier and
its value MUST be encoded as follows. The high-order 2 octets
will be 0x0000, and the low order 2 octets will be set to the
site-identifier to which this node belongs. All border
gateways MUST announce this value. We need the AS number and
the site identifier together to be automatically derivable to
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less than 6 octets; this enables for auto import and export of
routes (see the ES-Import RT definition in RFC7432 [RFC7432]).
* Reserved (1 octet): The low-order octets of the ESI Value will
be set to 0 on transmission and will be ignored on receipt.
Along with the RT-1 Ethernet A-D routes, border nodes MUST set the
second low order bit (Flags B0: Single Active, B1: MS-Border) of the
octet flag in the ESI Label Extended Community attribute that is
announced in tandem.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type=0x01 | Flags(1 octet)| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved=0 | ESI Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2
The site-identifier value is globally unique within the deployments.
The RT-1 Ethernet A-D route along with (i) the MS-Border bit being
set in the ESI Label Extended Community and (ii) the per-VNI RT
Extended Community will enable all BGs be aware of all the other BGs
in the network. All BGs are thus able to figure out other members in
the same site, and armed with this information is able to run a
Designated Forwarder (DF) election for BGs site and VNI scoped as
against the traditional Ethernet segment DF election. In Figure 1,
nodes BG-A1, BG-A2, BG-B1, BG-B2, BG-C1, and BG-C2, will announce the
ESI Label and the per-VNI RT Extended Communities. Nodes, BG-A1, and
BG-A2, will perform a DF election for Site-A, whereas, nodes BG-B1,
and BG-B2 will perform one for site-B. Even though, all BG nodes are
able to see all the advertisements, the site-identifier scopes the DF
election (using RT-4 ES Routes) to its site members. This
specification uses the All-Active Redundancy Mode specially when the
Anycast model of route announcements are used for the local routes.
4.2. Border Gateway Provisioning
Border Gateway nodes manage both the control-plane communications and
the data forwarding plane for any inter-site traffic. Once BGs are
discovered (using RT-1 routes), any RT-2/RT-5 routes from other sites
will be terminated and re-originated on such BGs. RT-2/RT-5 routes
carry downstream VNI labels. As BG discovery is agnostic to
symmetric or downstream VNI provisioning, rewriting next-hop
attributes before re-advertising these routes from other sites to a
given site provides flexibility to keep different mac-VRF or IP-VRF
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to VNI mapping in different sites and still able to interconnect L3
and L2 domains.
RT-1, RT-3, and RT-4 from other sites will be terminated at the BGs.
As has been defined in the specifications, RT-3 routes carry
downstream VNI labels and will be used to pre-build VXLAN tunnels in
the common EVPN domain for L2, L3, and Multi-Destination traffic.
4.2.1. Border Gateway Designated Forwarder Election
In the presence of more than one BG nodes in a site, forwarding of
multi-destination L2 or L3 traffic both into the site and out of the
site needs to be carried out by a single node. This node is termed
as a designated forwarder and elected per-VNI as per rules defined in
Section 8.5 of RFC7432 [RFC7432]. RT-4 Ethernet Segment routes are
used for the DF election. In the multi-site deployment, the RT-4
Ethernet Segment routes carry a ES-Import RT Extended Community
attribute with it. We need to enforce that these are imported to
only the local site members when the ES-Import value matches with its
own value. The 6-byte values are generated using a concatenation of
the 4-byte AS number the member belongs, with the 2-bytes of site-
identifier. As a result, only local site-members will match to form
the candidate list. All the BGs are able to extract the site
identifier from this attribute and the list of nodes where this
election is run is now constrained to the BGs between same site
members.
In both modes (Anycast and Multipath), RT-3 routes will be generated
locally and advertised by DF winner Border Gateway with unique
gateway IP. This will facilitate building fast converging flood
domain connectivity inter-site and intra-site and on same time
avoiding duplicate traffic by electing DF winner to forward multi-
destination inter-site traffic.
Failure events which lead to a BG losing all of its connectivity to
the IP interconnect backbone should trigger the BG to withdraw its
Border RT-4 Ethernet Segment route(s) and RT-1 A-D route, to indicate
to other BG's of the same site that it is no longer a candidate BG
and to indicate BG's of different sites that it is no longer a Border
Gateway.
4.2.2. Anycast Border Gateway
In this mode all BGs share same gateway IP and rewrite EVPN next-hop
attributes with a shared logical next-hop entity. However, these BGs
will maintain unique gateway IP to facilitate building IR trees from
site-local nodes to forward Multi-Destination traffic. EVPN RT-2,
RT-5 routes will be advertised to the nodes in the site from all
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other BGs and BG will run DF election per VNI for Multi destination
traffic. RT-3 routes will be advertised by the DF winner BG for a
given VNI so that only DF will receive and forward inter-site
traffic. It is also possible to advertise and draw traffic by all
BGs at a site to improve convergence properties of the network. In
case of multi-destination trees built by non-EVPN procedures (say
PIM), all BGs will receive but only DF winner will forward traffic.
It is recommended that BG be enabled in the Anycast mode wherein the
BG functionality is available to the rest of the network as a single
logical entity for inter-site communication. In the absence of
Anycast capability the BG could be enabled as individual gateways
(Single-Active BG) wherein a single node will perform the active BG
role for a given flow at a given time. As of now, the Border Gateway
system mac of the other border nodes belonging to the same site is
expected to be configured out-of-band.
4.2.3. Multi-path Border Gateway
In this mode, Border gateways will rewrite EVPN Next-hop attributes
with unique next-hop entities. This provides flexibility to apply
usual policies and pick per-VRF, per-VNI or per-flow primary/backup
border Gateways. Hence, an intra-site node will see each BG as a
next-hop for any external L2 or L3 unicast destination, and would
perform an ECMP path selection to load-balance traffic sent to
external destinations. In case an intra-site node is not capable of
performing ECMP hash based path-selection (possibly some L2
forwarding implementations), the node is expected to choose one of
the BG's as its designated forwarder. EVPN RT-2, RT-5 routes will be
advertised to the nodes in the site from all border gateways and
Border gateway will run DF election per VNI for Multi destination
traffic. RT-3 routes will be advertised by DF winner Border gateway
for a given VNI so that only DF will receive and forward inter-site
traffic. It is also possible to advertise and draw traffic by all
Border Gateways at a site to improve convergence properties of the
network. In case of multi-destination trees built by non-EVPN
procedures (say PIM), all border gateways will receive but only DF
winner will forward traffic.
4.3. EVPN route processing at Border Gateway
BG functionality in an EVPN site SHOULD be enabled on more than one
node in the network for redundancy and high-availability purposes.
Any external RT-2/RT-5 routes that are received by the BGs of a site
are advertised to all the intra-site nodes by all the BGs. For
internal RT-2/RT-5 routes received by the BG's from the intra-site
nodes, all the BGs of a site would advertise them to the remote BG's,
so any L2/L3 known unicast traffic to internal destinations could be
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sent to any one of the local BG's by remote sources. For known L2
and L3 unicast traffic, all of the individual BGs will behave either
as single logical forwarding node (Anycast model) or a set of active
forwarding nodes.
All control plane and data plane states are interconnected in a
complete downstream fashion. For example, BGP import rules for a
Type 3 route should be able to extend a flood domain for a VNI and
flood traffic destined to advertised EVPN node should carry the VNI
which is announced in Type 3 route. Similarly Type 2, Type 5 control
and forwarding states should be interconnected in a complete
downstream fashion.
o Route Target processing for RT-1 routes: Every IP-VRF and MAC-VRF
will generate RT-1 with the format described in section 4.1.
Route targets can be auto derived from Ethernet Tag ID (VLAN ID)
for that EVPN instance as described in section 7.10.1 of RFC7432
[RFC7432]. ES import route target extended community as described
in Section 7.6 of RFC7432 [RFC7432] is optional for RT-1 routes in
this context. ESI Label Extended Community Attribute is a MUST in
this context, since it carries the MS-Border notion as a new bit.
o Route Target processing for RT-4 routes: Every IP-VRF and MAC-VRF
will generate RT-4 with the format described in section 4.1.
Route targets can be auto derived from Ethernet Tag ID (VLAN ID)
for that EVPN instance as described in Section 7.10.1 of RFC7432
[RFC7432]. ES import route target extended community as described
in Section 7.6 of RFC7432 [RFC7432] is mandatory for RT-4 in this
context. The encoding of ES-Import is based on AS number and
Site-identifier as described in Section 4.2.1. Such import route
target will allow import of RT-4 only to the Border gateways of
same sites.
o Route Target processing for RT-2, RT-3, RT-5 routes: These routes
will carry either auto-derived route targets (based on Ethernet
Tag ID (VLAN ID) for that EVPN instance) or explicit route
targets. Border gateways usual import rules will imports these
routes and re-advertise these with border gateway next hops. Also
the routes which are imported at Border Gateways and re-advertised
SHOULD implement a mechanism to avoid looping of updates should
they come back at Border Gateways. RT-3 routes will be imported
and processed on border gateways from other border gateways but
MUST NOT be advertised again.
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4.4. Multi-Destination tree between Border Gateways
The procedures described here recommends building an Ingress
Replication (IR) tree between Border Gateways. This will facilitate
every site to independently build site-specific Multi destination
trees. Multi-destination end-to-end trees between leafs could be PIM
(site 1) + IR (between border Gateways) + PIM(site 2) or IR-IR-IR or
PIM-IR-IR. However this does not rule out using IR-PIM-IR or end-to-
end PIM to build multi-destination trees end-to-end.
Border Gateways will generate RT-3 routes with unique gateway IP and
advertise to Border Gateways of other sites. These RT-3 routes will
help in building IR trees between border gateways. However, only DF
winner per VNI will forward multi-destination traffic across sites.
As Border Gateways are part of both site-specific and inter-site
Multi-destination IR trees, split-horizon mechanism will be used to
avoid loops. Multi-destination tree with Border gateway as root to
other sites (or Border-Gateways) will be in a separate horizon group.
Similarity Multi-destination IR tree with Border Gateway as root to
site-local nodes will be in another split horizon group.
If PIM is used to build Multi-Destination trees in site-specific
domain, all Border gateway will join such PIM trees and draw multi-
destination traffic. However only DF Border Gateway will forward
traffic towards other sites.
4.5. Inter-site Unicast traffic
As site-local nodes will see all inter-site EVPN routes via Border
Gateways, VXLAN tunnels will be built between leafs and site-local
Border Gateways and Inter-site VXLAN tunnels will be built between
Border gateways in different sites. An end-to-end VXLAN
bidirectional forwarding path between inter-site leafs will consist
of VXLAN tunnel from leaf (say Site A) to its Border Gateway (BG-A1),
another VXLAN tunnel from Border Gateway (BG-A1) to Border Gateway
(BG-B1) in another site (say site B) and Border gateway (BG-B1) to
leaf (in site B). Such an arrangement of tunnels is scalable as a
full mesh of VXLAN tunnels across inter-site leafs is substituted by
combination of intra-site and inter-site tunnels.
L2 and L3 unicast frames from site-local leafs will reach border
gateway using VXLAN encapsulation. At Border gateway, VXLAN header
is stripped out and another VXLAN header is pushed to sent frames to
destination site Border Gateway. Destination site Border gateway
will strip off VXLAN header and push another VXLAN header to send
frame to the destination site leaf.
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4.6. Inter-site Multi-destination traffic
Multi-destination traffic will be forwarded from one site to other
site only by DF for that VNI. As frames reach Border Gateway from
site-local nodes, VXLAN header will be decapsulated from the payload,
and encapsulated with another VXLAN header (derived from downstream
Type 3 EVPN routes received from the border gateways of the
destination site) to forward the payload to the destination site
border gateway. Similarly destination site Border Gateway will strip
off VXLAN header and forward the payload after encapsulating with
another VXLAN header towards the destination leaf.
As explained in Section 4.4, split horizon mechanism will be used to
avoid looping of inter-site multi-destination frames.
4.7. Host Mobility
Host movement handling will be same as defined in RFC7432 [RFC7432].
When host moves, EVPN RT-2 routes with updated sequence number will
be propagated to every EVPN node. When a host moves inter-site, only
Border gateways may see EVPN updates with both next-hop attributes
and sequence number changes and leafs may see updates only with
updated sequence numbers. However in other cases, both Border
gateway and leaves may see next-hop and sequence number changes.
5. Convergence
5.1. Fabric to Border Gateway Failure
If a Border Gateway is lost, Border gateway next-hop will be
withdrawn for RT-2/RT-5 routes. Also per-VNI DF election will be
triggered to chose new DF. DF new winner will become forwarder of
Multi-destination inter-site traffic.
5.2. Border Gateway to Border Gateway Failures
In case where inter-site cloud has link failures, direct forwarding
path between border gateways can be lost. In this case, traffic from
one site can reach other site via border gateway of an intermediate
site. However, this will be addressed like regular underlay failure
and traffic terminations end-points will still stay same for inter-
site traffic flows.
6. Interoperability
The procedures defined here are only for Border Gateways. Therefore
other EVPN nodes in the network should be RFC7432 [RFC7432] compliant
to operate in such topologies.
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As the procedures described here are applicable only after receiving
Border A-D route, if other domains are connected which are not
capable of such multi-site gateway model, they can work in regular
EVPN mode. The exact procedures will be detailed in a future version
of the draft.
The procedures here provides flexibility to connect non-EVPN VXLAN
sites by provisioning Border Gateways on such sites and inter-
connecting such Border Gateways by Border Gateways of other sites.
Such Border Gateways in non-EVPN VXLAN sites will play dual role of
EVPN gateway towards common EVPN domain and non-EVPN gateway towards
non-EVPN VXLAN site.
7. Isolation of Fault Domains
Isolation of network defects requires policies like storm control,
security ACLs etc to be implemented at site boundaries. Border
gateways should be capable of inspecting inner payload of packets
received from VXLAN tunnels and enforce configured policies to
prevent defects percolating from one part to rest of the network.
8. MVPN with Multi-site EVPN
BGP based MVPN as defined in RFC6513 [RFC6513] and RFC6514 [RFC6514]
will coexist with Multisite-EVPN with out any changes in route types
and encodings defined for MVPN route types in these RFCs. Route
Distinguisher and VRF route import extended communities will be
attached to MVPN routes as defined in the BGP MVPN RFCs. Import and
Export Route targets will be attached to MVPN routes either by Auto-
generating them from VNI or by explicit configuration per MVPN.
Since, BGP MVPN RFC adapts to any VPN address family to provide RPF
information to build C-Multicast trees, EVPN route types will be used
to provide required RPF information for Multicast sources in MVPNs.
In order to follow segmentation model of Multisite-EVPN, following
procedures are recommended to build provider and customer multicast
trees between sources and receivers across sites.
8.1. Inter-Site MI-PMSI
As defined in above mentioned MVPN RFCs, I-PMSI A-D routes are used
to signal a provider tunnel or MI-PMSI per MVPN. Multisite-EVPN
recommends EVPN Type-3 routes to build such MI-PMSI provider tunnel
per VPN between Border Gateways of different sites. Every MVPN node
will use its unique router identifier to build these MI-PMSI provider
tunnels. In Anycast Border gateway model also, these MI-PMSI
provider tunnels are built using unique router identifier of Border
gateways. In similar fashion, these Type-3 routes can be used to
build MI-PMSI provider tunnel per MVPN with in sites.
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8.2. Stitching of customer multicast trees across sites
All Border Gateways will rewrite next-hop and re-originate MVPN
routes received from other sites to local site and from local site to
other sites. Therefore customer Multicast trees will be logically
built end-to-end across sites by stitching these trees via Border
gateways. A C-multicast join route (say Type 7 MVPN) will follow
EVPN RPF path to build C-multicast tree from leaf in a site to its
Border gateway and to destination site leafs via destination site
Border Gateways. Similarly Source-Active A-D MVPN route (Type 5
MVPN) will be rewritten with next-hop and re-originated via Border
gateways so that source C-Multicast trees will be stitched via Border
gateways.
8.3. RP placement across sites
Multisite-EVPN recommends only Source C-Multicast trees across sites.
Therefore Customer RP placement per MVPN should be restricted with in
sites. Source-Active A-D MVPN route type (Type 5) will be used to
signal C-Multicast sources across sites.
8.4. Inter-Site S-PMSI
As defined in BGP MVPN RFCs, S-PMSI A-D routes (Type 3 MVPN) will be
used to signal selective PMSI trees for high bandwidth C-Multicast
streams. These S-PMSI A-D routes will be signaled across sites via
Border gateways rewriting next-hop and re-originating them to other
sites. PMSI tunnel attribute in re-originated S-PMSI routes will be
adjusted to the provide tunnel types between Border gateways across
sites.
9. Observations with Multi-site EVPN
Since an Anycast address is now advertised in the underlay protocols
per ES, this solution does increase the scale of routes for the
underlay. Furthermore, the ES failures are now conveyed via the
underlay protocols. To drop down to single homing mode, one would
need to track the interfaces that are used for the inter-site
traffic. It is a requirement to not have intra-site and inter-site
traffic use the same links from the nodes. Due to the anycast
formulation of the gateways, it is not possible to entertain any
load-balancing per ES link for the gateway nodes.
Loop avoidance by the use of the domain-path-id as defined in
[EVPN-IPVPN-INTERWORKING] will be detailed in a future version of the
draft.
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10. Acknowledgements
This authors would like to thank Max Ardica, Murali Garimella, Anuj
Mittal, Lilian Quan, Veera Ravinutala, Tarun Wadhwa for their review
and comments.
11. IANA Considerations
TBD.
12. Security Considerations
TBD.
13. References
13.1. Normative References
[DCI-OVERLAY]
A. Sajassi et. al., "A Network Virtualization Overlay
Solution using EVPN", 2018, .
[EVPN-IPVPN-INTERWORKING]
A. Sajassi et. al., "EVPN Interworking with IPVPN", 2018,
.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, .
13.2. Informative References
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, .
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
.
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[RFC7209] Sajassi, A., Aggarwal, R., Uttaro, J., Bitar, N.,
Henderickx, W., and A. Isaac, "Requirements for Ethernet
VPN (EVPN)", RFC 7209, DOI 10.17487/RFC7209, May 2014,
.
[RFC8365] Sajassi, A., Ed., Drake, J., Ed., Bitar, N., Shekhar, R.,
Uttaro, J., and W. Henderickx, "A Network Virtualization
Overlay Solution Using Ethernet VPN (EVPN)", RFC 8365,
DOI 10.17487/RFC8365, March 2018,
.
Appendix A. Additional Stuff
TBD.
Authors' Addresses
Rajesh Sharma (editor)
Cisco Systems
170 W Tasman Drive
San Jose, CA
USA
Email: rajshr@cisco.com
Ayan Banerjee (editor)
Cisco Systems
170 W Tasman Drive
San Jose, CA
USA
Email: ayabaner@cisco.com
Ali Sajassi
Cisco Systems
170 W Tasman Drive
San Jose, CA
USA
Email: sajassi@cisco.com
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Lukas Krattiger
Cisco Systems
170 W Tasman Drive
San Jose, CA
USA
Email: lkrattig@cisco.com
Raghava Sivaramu
Cisco Systems
170 W Tasman Drive
San Jose, CA
USA
Email: raghavas@cisco.com
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